1. Field of invention
This invention relates to knit therapeutic compression stockings for use primarily by patients to apply compressive forces to their leg(s) to reduce to possibility of thromboemoblisms. More particularly, this invention relates to therapeutic knit stockings having frictional surfaces on the foot portion of the stocking to prevent slipping by the patient when walking on a floor.
2. Prior Art
Therapeutic or anti-embolism stockings are used to apply compressive force to the wearer's leg. This force is usually applied in the form of a pressure gradient which decreases progressively from the ankle to the upper thigh of the leg. Such stockings are designed to increase the velocity of the blood flowing through the leg thereby reducing the probability of thromboembolism. Therapeutic stockings have found general use in hospitals to reduce the chances of embolism in post-operative and bed-ridden patients. However, because the stockings are used in a hospital environment, there exists a tendency for them to be worn without other footwear. Because of this, there is an increased possibility that an ambulatory patient could slip on the smooth hospital floors. Therefore, anti-slip means have been developed to minimize the danger of a patient's slipping while wearing the stocking.
Prior art such as that in U.S. Pat. No. 4,021,860 issued to Swallow et al. provides an anti-slip feature by fusing a thermoplastic material to the bottom or foot of the stocking. However, because the anti-slip feature is not integrally knit into the stocking, an extra step is required in the manufacturing process to remove the stocking from the knitting machine and place it in an apparatus to fuse the thermoplastic material to foot of the stocking. This extra step increases the cost of manufacturing making it less economically desirable. Additionally, since the anti-slip feature was fused to the outer surface of the stocking, it is susceptible to delaminating after extensive use or repeated washings. More importantly, the thermoplastic material is relatively inelastic and when fused to the stocking it would impair the stretch characteristics of the stocking thereby limiting the ability of the stocking to function for the purpose for which it was primarily designed.
Subsequent prior art such as that in U.S. Pat. No. 4,149,274 issued to Garrou et al. recognized the limitations in affixing the anti-slip means to the outer surface of the stocking and provided an improved anti-slip means which was incorporated into the stocking during the knitting of the stocking. Garrou et al. describes an anti-slip means wherein friction yarns, such as an uncovered spandex, are interknit with the stocking's body yarn using tuck and float stitching. These stitches form unknit portions of friction yarn on the interior surface of the stocking during knitting. The stocking is then everted to expose these unknit portions of friction yarn which form the anti-slip means. These unknit friction yarns engage the floor to minimize slippage. However, as with the earlier prior art, an extra manufacturing step is required to expose the anti-slip means. Additionally, the unknit portions of friction yarn, while acting as an anti-slip means, can also increase the probability that the unknit yarns will snag on a rough surface resulting in either a damaged stocking or perhaps tripping the patient. Thus, although the prior art has been somewhat successful in providing an anti-slip feature for therapeutic stockings, there still exist significant disadvantages in the prior art. The present invention provides a distinct advantage over the prior art by using an integrally knit design which does not require the knit stocking to be everted nor does it leave unknit yarns on the exterior surface which could cause the stocking to snag.